1. Field of the Invention
This invention relates to a metal-made honeycomb body, which is adapted to support thereon an exhaust gas cleaning catalyst and is generally used in an exhaust gas purifying system of an automotive vehicle.
More specifically, this invention is concerned with an economical honeycomb body excellent in properties such as durability and featuring the use of one or more wire arrangements, each of which is formed of wires, in place of a like number of conventional, costly, heat-resistant planar band(s) or corrugated band(s).
2. Description of the Related Art
Known catalyst supports of the above-described type for exhaust gas cleaning systems include two types, one being ceramic monolithic supports making use of a ceramic material such as cordierite and the other metallic monolithic supports made of a metal.
Especially in recent days, a great deal of research and development work has been being concentrated on metal-made monolithic supports with a view toward improving their drawbacks, in other words, from the viewpoints of mechanical strength, durability, flow resistance, cleaning efficiency (size reduction) and the like.
A metal-made catalyst support of the type described above, which may hereinafter be called a "metal support" for the sake of brevity, is constructed as shown in FIG. 4 or FIG. 5, that is, by a metal-made honeycomb structure H (which may hereinafter be called the "metal-made honeycomb body" or simply the "honeycomb body") and a cylindrical metal casing 4 opening at opposite ends thereof and fixedly enclosing the honeycomb body H therein. In general, the honeycomb body H is fabricated by stacking a planar band 1, which is made of a heat-resistant steel sheet, and a corrugated band 2, which has been formed by corrugating a similar heat-resistant steel sheet, one over the other in a mutually continuous relation, and then rolling them together into a spiral form or by alternately stacking such planar bands 1 and corrugated bands 2 one over the other into a multilayered form, so that the honeycomb body H defines a number of network-patterned, axial gas flow passages (hereinafter called "cells") for permitting passage of exhaust gas therethrough.
Incidentally, FIG. 4 illustrates the rolled honeycomb body H while FIG. 5 depicts the stacked honeycomb body H.
The honeycomb body and the metal casing are then firmly fixed together by brazing or welding them so that the honeycomb body can withstand thermal expansions and thermal stresses--which occur due to the high temperature of exhaust gas itself and an exothermic reaction of the exhaust gas by the exhaust gas cleaning catalyst--and also extreme vibrations during running of the automotive vehicle. Needless to say, each planar band and its associated corrugated band, which form the honeycomb body, can be fixed together at areas of contact therebetween by various methods.
As the planar band(s) 1 and the corrugated band(s) 2 in the above-described conventional honeycomb body H, it is possible to use bands having a thickness not greater than 0.1 mm and made of a material such as heat-resistant stainless steel, e.g., chromium steel (chromium content: 13-25%) or Fe-20%Cr-5%Al, or stainless steel formed by adding one or more rare earth meal to the former stainless steel to improve the high-temperature oxidation resistance. Al-containing steel bands are extremely preferred, because they have improved high-temperature oxidation resistance and, when subjected to heat treatment, .alpha.-Al.sub.2 O.sub.3 is caused to deposit in various forms such as whisker and mushroom forms on their surfaces and can serve to firmly hold a wash coat capable of carrying exhaust gas cleaning catalysts such as Pt, Pd and Rh.
The planar bands 1 and corrugated bands 2, which make up the metal-made honeycomb body H, are however extremely costly, thereby reducing the price competitive power of the metal-made honeycomb body compared with ceramic-made honeycomb bodies.